A sigmoid volvulus is a twisting of the sigmoid colon, the S-shaped section of your large intestine just above the rectum, around the tissue that holds it in place. This twisting creates a closed-loop obstruction, meaning nothing can pass through, and it can cut off blood supply to the affected segment. It’s the most common type of colonic volvulus and accounts for a significant share of large bowel obstructions, particularly in certain parts of the world.
How the Twisting Happens
Your sigmoid colon hangs from a fan-shaped fold of tissue called the mesentery, which anchors it to the back wall of your abdomen. In some people, the sigmoid colon is longer than average, or the mesentery is loose enough to let the colon move more freely than it should. When the sigmoid loop rotates around its mesenteric base, it pinches shut at the point of the twist, trapping gas and stool inside.
The trapped contents cause the loop to swell dramatically. As pressure builds, blood flow through the mesenteric vessels slows and eventually stops. Without blood, the bowel wall begins to die. This progression from obstruction to tissue death is the central danger of a sigmoid volvulus. If the bowel becomes gangrenous or perforates, stool can leak into the abdominal cavity and cause peritonitis, a life-threatening infection.
Who Gets Sigmoid Volvulus
The condition looks remarkably different depending on where in the world it occurs. In Western countries, the typical patient is in their 70s or 80s, and men and women are affected equally. In African, Asian, Middle Eastern, Eastern European, and South American countries, sigmoid volvulus is far more common overall, patients tend to be younger, and most are male.
Chronic constipation is the most consistent risk factor across populations. Years of straining and stool buildup gradually stretch and elongate the sigmoid colon and its mesentery, creating the redundant, mobile loop that’s prone to twisting. In developing nations, high-fiber diets can overload the sigmoid colon with bulk, producing a similar effect through a different mechanism.
People living in nursing homes or psychiatric care facilities are disproportionately affected. Between 25% and 35% of all volvulus patients are admitted from neuropsychiatric institutions, and another 10% to 15% come from long-term nursing facilities. The combination of prolonged bed rest, chronic constipation, and medications that slow gut motility (especially certain psychiatric drugs) creates ideal conditions for the sigmoid to twist. Neurological conditions like Parkinson’s disease, multiple sclerosis, and spinal cord injuries also raise risk for the same reasons.
Pregnancy is another recognized trigger. A growing uterus shifts the position of abdominal organs, and up to 45% of pregnant patients who develop a large bowel obstruction have sigmoid volvulus specifically. Large ovarian tumors and other pelvic masses can displace the sigmoid colon enough to cause torsion in a similar way. In parts of South America where Chagas disease is endemic, the infection damages nerves in the colon wall, producing a massively enlarged colon (megacolon) that predisposes to volvulus in as many as 30% of affected patients.
Symptoms to Recognize
The classic presentation is abdominal pain, distension, and an inability to pass gas or stool. The abdomen can become visibly swollen, sometimes dramatically so, because the trapped loop fills with gas. Nausea and vomiting often follow as the obstruction prevents anything from moving through. In older or institutionalized patients, symptoms can develop gradually over days, making the condition easy to mistake for routine constipation.
When the blood supply is compromised, the pain intensifies and becomes more constant. Fever, rapid heart rate, and signs of shock suggest the bowel wall has died or perforated. At that point, the situation becomes a surgical emergency.
How It’s Diagnosed
A plain abdominal X-ray is the first imaging step and can confirm the diagnosis in 60% to 70% of cases. The hallmark finding is the “coffee bean sign,” a massively distended sigmoid loop that takes on an inverted U shape resembling a large coffee bean. The two limbs of the twisted loop rise up out of the pelvis, often reaching the upper abdomen.
In 20% to 30% of patients, the limbs overlap or angle to one side, making the X-ray harder to read. When the plain film isn’t clear, a CT scan provides more detail. CT can show the “whirl sign,” a pattern created by the mesentery and its blood vessels spiraling around the point of torsion. CT also reveals whether the bowel wall has lost its blood supply, which directly changes the treatment plan.
Initial Treatment: Endoscopic Untwisting
If there are no signs of peritonitis or dead bowel, the first step is to untwist the sigmoid without surgery. A doctor passes a flexible scope (sigmoidoscope or colonoscope) into the rectum and advances it to the point of the twist. Gentle pressure and air insufflation can coax the loop to untwist. Once the colon opens, a tube is left in place through the rectum to keep the bowel decompressed and prevent immediate re-twisting.
This approach is effective as an initial measure, but it does not fix the underlying problem. The elongated, mobile sigmoid colon remains, and the volvulus has a high tendency to recur. For that reason, surgeons generally plan a definitive operation during the same hospital stay, after the bowel has been decompressed and the patient stabilized. If endoscopic untwisting fails, surgery becomes necessary right away.
When Surgery Is Needed
Surgery is required in three situations: when endoscopic decompression doesn’t work, when the bowel shows signs of gangrene or perforation, or as a planned procedure after successful untwisting to prevent recurrence. The operation involves removing the sigmoid colon segment that’s prone to twisting.
What happens next depends on the condition of the remaining bowel and the patient’s overall stability. If the bowel ends look healthy, there’s no significant contamination in the abdomen, and the patient is stable, the surgeon reconnects the two ends immediately. This restores normal bowel continuity in a single operation.
If the bowel is gangrenous, the abdomen is contaminated with stool, or the patient is too unstable for a longer procedure, the surgeon performs a two-stage approach. The twisted segment is removed, and the upstream end of the colon is brought through the abdominal wall to create a temporary stoma (an opening where stool empties into a bag). After 3 to 6 months of recovery, a second surgery can reconnect the bowel, though not every patient is healthy enough for that reversal.
Sigmoid vs. Cecal Volvulus
The cecum (the pouch where the small intestine meets the large intestine) can also twist, but cecal volvulus behaves differently. Sigmoid volvulus involves a counterclockwise twist at the base of the mesentery, while cecal volvulus rotates clockwise and involves the cecum, ascending colon, and the end of the small intestine. Cecal volvulus cannot be treated with endoscopic untwisting and requires surgery from the start. On imaging, the two look quite different: sigmoid volvulus produces the coffee bean shape rising from the pelvis, while cecal volvulus creates a dilated loop in a different location, often the left upper abdomen.
A rarer and more dangerous relative is the ileosigmoid knot, where the small intestine wraps around the base of the sigmoid colon. This causes sudden, severe pain and rapid shock, and it requires emergency surgery without any attempt at endoscopic treatment.